ARM: sun7i/sun6i: irqchip: Add irqchip driver for NMI controller

ARM: sun7i/sun6i: irqchip: Add irqchip driver for NMI controller

Allwinner A20/A31 SoCs have special registers to control / (un)mask /
acknowledge NMI. This NMI controller is separated and independent from GIC.
This patch adds a new irqchip to manage NMI.

Signed-off-by: Carlo Caione <carlo@caione.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-sunxi@googlegroups.com
Cc: mark.rutland@arm.com
Cc: hdegoede@redhat.com
Link: http://lkml.kernel.org/r/1395256879-8475-2-git-send-email-carlo@caione.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>